LEWISBORO – The Katonah-Lewisboro school district is examining five buildings after it was notified last week by the state Department of Labor of an anonymous complaint about the possibility of mold in the schools. It has hired an environmental engineering firm to perform air-quality tests. Five of the district's six buildings are being tested and results are expected by the end of the week.

So what's at issue?

We talk to Robert Weitz, principal of RTK Environmental Group in White Plains, a certified microbial investigator by the American Council for Accredited Certification. His company consults in mold, lead, asbestos, water, soil and indoor air quality.

Q: How can you tell if your building has mold? What should you look for?

A: It's always best to use your senses when "looking" for mold. Mold comes in a variety of colors, shapes and sizes. Mold prefers to grow in cool, dark and damp locations, such as a basement, HVAC duct or a wall or floor cavity. Start with your eyes; visible mold on a wall or ceiling is usually just the tip of the iceberg. We'll often find that an entire wall cavity is impacted. You should also be guided by your sense of smell. If you smell a musty odor, that's a sign of mold. If you smell mildew, mildew is actually mold. And also be aware of symptoms like respiratory ailments, headaches, unexplained rashes that seem to be more acute when you're in one location rather than another.

Q: What causes mold?

A: Mold spores are naturally occurring in the environment and are usually harmless. They enter a building or home through doors and windows, through HVAC units, and are tracked in on your shoes and clothes. Mold becomes problematic when it colonizes. To colonize, mold needs two things: A source of moisture and something to feed on. Homes and buildings have plenty for mold to feast on like leaky pipes, condensation, a flooded basement or bathroom, carpeting, wood, fabrics and other materials.

Q: Are there acceptable levels of mold? If so, how do you define that?

A: As part of a mold investigation, we take several air samples inside the structure to gauge mold spore counts. We also compare it to an air sample taken outdoors — a baseline — to see if an elevated level is detected. The amount and types will fluctuate from structure to structure.

Q: Can mold be dangerous?

A: Mold can be dangerous, but it depends on whether the mold sampled is toxic — meaning it contains poisonous mycotoxins — or is an allergen. Mold can cause chronic allergies, headaches, fatigue, rashes, throat and eye irritations, and, in serious cases, mold causes pneumonitis and triggers asthma. It's important to note that toxic mold can come in any color — black, green, blue, orange, white, even pink — and, contrary to media reports, not all black mold is toxic. But mold colonies are unhealthy and should be removed from inside a structure expertly and carefully so as to not cross-contaminate clean rooms with spores.

Q: How does remediation work?

A: The first step is to have your property properly tested for mold. You'll receive a detailed report detailing the type of mold detected (if any) and its location (if applicable). The report provides a remediation plan detailing the best method for drying the area, removal of walls, floors and ductwork (when applicable); which contents must be scrapped (boxes, furniture, appliances); and what's salvageable. There are some great remediation companies that specialize in working with mold. They properly set up a containment area and create negative air pressure to prevent cross-contamination.

Q: When hiring an inspection or remediation company, what should consumers watch out for?

A: Mold remediation is an unregulated industry and there are plenty of charlatans out there. But there are reputable remediation contractors that we often refer clients to. Consumers should protect themselves by first calling an independent inspection company to perform a mold investigation.

Never hire a "one-stop shop" that offers both mold testing and remediation, because it's a complete conflict of interest. Having an independent test performed first will not only provide you with an accurate, unbiased test, you'll save thousands of dollars (in many cases, five figures) by avoiding exaggerated repair estimated or an improper or ineffective remediation.